Communication devices such as wireless devices are also known as e.g. user equipments (UE), mobile terminals, wireless terminals, and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, laptops, tablet computers or surf plates with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an network node. A cell is the geographical area where radio coverage is provided by the network node.
The network node may e.g. be a base station such as a Radio Base Station (RBS), eNB, eNodeB, NodeB, node B, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size.
Further, each network node may support one or several communication technologies. The network nodes communicate over the air interface operating on radio frequencies with the wireless terminals within range of the network node. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission in LTE is controlled by the radio base station.
With radio networks like those used for LTE and other cellular technologies becoming more complex, network planning needs to be made easier—planning, configuration, management, optimization and healing all need to be automated to bring improvements. As a result, the concept of Self-Organizing Networks (SON) is growing in interest and use. With the networks themselves being able to monitor performance, they can optimize themselves to be able to provide the optimum performance. The self-organization capability of a mobile network mainly includes three aspects: self-configuration, self-optimization, and self-healing.
Self-optimization refers to the ability of the network to adapt itself to surrounding conditions and optimize its performance based on coverage, capacity, handover between cells, and interference. Two key SON functions are Load Balancing (LB) and interference mitigation. With LB, traffic load, such as wireless devices, may be moved between cells and frequencies with the aim to distribute traffic load evenly in the network. Overloaded network cells may thereby offload excess traffic to low-loaded adjacent cells.
When a certain cell is over-loaded, a number of wireless devices connected to that cell, the source cell, might need to be moved to neighboring cells. Before selecting a target cell to which a wireless device should be moved for load balancing reasons, the wireless device needs to perform measurements for neighboring cells. These measurements are sometimes referred to as UE measurements. A wireless device may be configured to perform inter-frequency measurements in order to search for a target cell within the same Radio Access Technology (RAT) as the RAT of the source cell. A wireless device may also be configured to perform Inter RAT (IRAT) measurements in order to search for a target cell within a RAT different from the one of the source cell.
The network may select a number of wireless devices to perform such measurements for neighboring cells. This selection of wireless devices may be made at random, which is in-efficient in many scenarios and might lead to non-optimal network performance such as lower end-user and system throughput, higher latency and lower utilization of network resources.